Cell Division and Geneties Page 4-45 EXTRA CREDIT-PEDIGREE ANALYSIS OF X-LINKED

Question

Cell Division and Geneties Page 4-45 EXTRA CREDIT-PEDIGREE ANALYSIS OF X-LINKED TRAITS (5 points) Your instructor MAY assign this extra credit activity. Each instructor has a different method for determining if extra credit will be accepted and how many extra credit points are possible. Check with your instructor before doing any extra credit assignments in this outline. 1. Go to the following web site: http://www.biology.arizona.edu/human_bio/problem_sets/color_blindnes s/color blindness.html You should be on a page entitled "Color Blindness Problem Set. 2. Read the introduction, which contains information about the history of color blindness in Audrei's family. At the bottom of the page, click on "Brief introduction to sex-linked inheritance" Review the information in this section. 4. At the bottom of the page, click on "Color Blindness Problem Set." At the bottom of the page, click on "Begin Problem Set. 5. Complete wly roblems 1-4 of the problem set Hint: The term hemizygous refers to a person who has only one of the usual two alleles for a trait. For example, males have only one allele for sex-linked traits (the allele on the X chromosome), with no matching allele on the Y chromosome.

Explanation / Answer

Red-green color blindness is an X-linked recessive trait. Since male carry only one X-chromosome and if this chromosome has the allele for red-green color blindness, the male will have the defect in color perception. Contrary to this, females carrying two X-chromosomes must possess the defective recessive allele on both the chromosomes to be red-green color blind. Females with one mutant allele and one normal allele are carriers and are not color blind. However, they can pass the trait of color blindness to their offsprings.

Based on the questions posted on the link, Caroline is a carrier for color blindness with the defective allele inherited from her mother and normal allele from father.

Representing the normal dominant allele as XR and recessive mutant allele as Xr;

The genotype of Caroline and her husband would be XrXR and XRY.

Thus,

Genotype of Caroline : XrXR

Genotype of husband : XRY

Probability of color blind daughter : 0 (carrier or nomal daughter based on the gametes from the parents)

Probability of color blind son : 1/2 = 0.5 (one of the two sons can be color blind due to the carrier nature of the mother).

XR Y Xr XrXR (carrier daughter) XrY (Color blind son) XR XRXR (Normal daughter) XRY (Normal son)

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